(1) Field of the Invention
The present invention relates to a digital multiplex radio system using microwaves in a Synchronous Digital Hierarchy (SDH) communication network and, more particularly, to a digital multiplex radio system which, having a plurality of active lines and at least one spare line, transmits and receives radio signals with a Synchronous Transfer Mode (STM) signal used as a base band signal.
(2) Description of the Related Art
Concerning a public communication network of trunk line and branch line systems, a demand for unifying international interfaces for wide band communication service has recently been increased and the SDH was standardized by the International Telecommunications Union (ITU). The microwave multiplex radio system based on this standard presents a problem in that the hardware is usually large.
Conventionally, the multiplex radio system is composed of a transmitting section, receiving section, modulating section, demodulating section, base band processing section, switching section having a transmission switching function and a receiving end switching function, supervisory function section, circuit control section, timing clock supply section, order-wire communication function section, Data Communication Channel (DCC) processing section, and so on, and each of these sections is contained in a separate independent case. Usually, the case is of a card shape, and mounted in a slot in a rack. A back wire board provided at the inner part of slot connects respective cards to each other. However, the receiving section is connected to the demodulating section and the modulating section is connected to the transmitting section via a high-frequency coaxial cable, and the supervisory section and circuit control section are connected respectively to an opposite card via a cable with mulipin connector as well as the back wire board.
In the above-described conventional multiplex radio system, however, since the respective principal sections constituting the system are contained in a separate independent case, a wide installation space is required as the whole system, posing problems of installation space and wiring cost. Further, the signals with a different speed are sent complicatedly over a long distance by using the wiring, resulting in a problem of electro magnetic interference caused on other equipment and systems.
Also, when the sections constituting the system are divided finely and each of them is contained in a separate independent case, a repair of fault often requires much time if the system fails. That is, because a rapid repair of fault is desired if the system fails, on the occurrence of fault a maintenance personnel, taking a set of normal cases, hastens to the failed system. He replaces respective cases suspected to have a fault in the failed system one after another with a normal corresponding case to hastily carry out the repair of fault. However, the number of cases are large because the sections constituting the system are divided finely, so that it sometimes takes much time to find the faulty case.
Further, in the SDH communication system, the supervision of state must be exercised for each independent unit (card). Therefore, a lot of alarm information is collected in the supervisory function section from the divided units, posing a problem of great processing load of the supervisory function section.